Sunday, November 22, 2009

The Extrastriate Body Area and Visual Distortions in Anorexia

Contour Drawing Rating Scale (Thompson & Gray, 1995) - established as a reliable and valid measure of body size perception.

Anorexia nervosa, an obsessive and unrelenting quest for thinness, is one of the most deadly psychiatric disorders. The documented mortality rate ranges from 3.3% to 18% in different studies (Herzog et al., 2000), and those with the disorder are ten times more likely to die from their illness than a comparable healthy population. A severe distortion of body image is a cardinal feature of anorexia:
Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or denial of the seriousness of the current low body weight.
An excellent recent review covered the alterations in widespread neural circuits observed in those with anorexia, along with abnormalities in the neurotransmitters serotonin and dopamine (Kaye et al., 2009):
New brain imaging technology provides insights into ventral and dorsal neural circuit dysfunction — perhaps related to altered serotonin and dopamine metabolism — that contributes to the puzzling symptoms found in people with eating disorders. For example, altered insula activity could explain interoceptive dysfunction, and altered striatal activity might shed light on altered reward modulation in people with anorexia nervosa.
Another angle to examine is the reason for such pervasive distortions of self-image. Are there literally changes in visual cortex function that correlate with this symptom?

But first, a few words on some confusing neuroanatomical terminology. The striatum is a subcortical structure that consists of the caudate nucleus and the putamen. As mentioned above, the striatum is involved in reward processing (among other things). On the other hand, the primary visual cortex, or V1 (at the back of the occipital lobe) is sometimes referred to as striate cortex. Higher levels of visual cortex beyond V1 are known as extrastriate cortex. And there is where our story begins.

In 2001, an fMRI study demonstrated that a specific region in extrastriate cortex, in the lateral occipitotemporal cortex, showed selective responses to pictures of bodies and body parts relative to other types of visual stimuli (Downing et al., 2001). The authors dubbed this region the "extrastriate body area" (EBA). An earlier study in epileptic patients (McCarthy et al., 1999) found regions that showed selective responses to hands, relative to faces and objects (they didn't test other body parts). Instead of using fMRI, McCarthy and colleagues recorded from electrode grids placed directly on the cortical surface for the purpose of monitoring for seizures, prior to surgical resection of the epileptogenic tissue. They observed a specific electrophysiological response, which was evoked 230 msec after the subjects viewed pictures of hands.

So the question arises, are there neuroanatomical and functional changes in the extrastriate body area of individuals with anorexia? Suchan et al. (2009) quantified the structural MRIs of 15 women with anorexia and 15 healthy control women. They also localized the EBA using functional MRI -- participants viewed the stimuli used in the study of Downing et al. (freely available for download). The participants also completed the Contour Drawing Rating Scale, and the scores were compared to those given by 10 independent female raters who viewed photos of the subjects.

Not surprisingly, the women with anorexia (BMI=16.0, see images of Christian Bale in Anorexia, Insomnia, and Paranoia for an example) overestimated their body size. Conversely, the healthy women (BM=22.0) underestimated their body size. And using a whole-brain voxel-based morphometric analysis, gray matter density was indeed reduced in the left EBA of the anorexic participants.

Fig. 2 (Suchan et al. (2009). Activation of the extrastriate body area (EBA) localizer scans from healthy age matched controls (blue), women with anorexia nervosa (AN; green) and reduction of gray matter in the EBA of the AN group (white). Overlap between EBA activation of healthy, age matched controls and AN is coloured in light-blue.

Of course, whether the neuroanatomical change is a cause or an effect of the disease is unknown, as acknowledged by the authors:
Although the present study is the first to demonstrate focused gray matter volume reduction in the EBA, several open questions remain. First, the causality is unclear. Future studies using a longitudinal design should focus on the question of whether the EBA volume reductions precede the onset of the AN and therefore might be of etiological relevance or whether they are a result of the disorder.
Nevertheless, preliminary evidence supports a role for visual perceptual deficits contributing to body image distortion in anorexia nervosa.

I'll leave you with the music video for Tunic (Song for Karen) by Sonic Youth. It's a weirdly arty but touching depiction of Karen Carpenter's struggle with anorexia and bulimia, with Kim Gordon as Karen.

dreaming, dreaming of a girl like me
hey what are you waiting for - feeding, feeding me
I feel like I'm disappearing - getting smaller every day
but I look in the mirror - I'm bigger in every way


Downing PE, Jiang Y, Shuman M, Kanwisher N. (2001). A cortical area selective for visual processing of the human body. Science 293:2470-3.

Herzog DB, Greenwood DN, Dorer DJ, Flores AT, Ekeblad ER, Richards A, Blais MA, Keller MB. (2000). Mortality in eating disorders: a descriptive study. Int J Eat Disord. 28:20-6.

Kaye WH, Fudge JL, Paulus M. (2009). New insights into symptoms and neurocircuit function of anorexia nervosa. Nat Rev Neurosci. 10:573-84.

McCarthy G, Puce A, Belger A, Allison T. (1999). Electrophysiological studies of human face perception. II: Response properties of face-specific potentials generated in occipitotemporal cortex. Cereb Cortex 9:431-44.

Suchan, B., Busch, M., Schulte, D., Grönermeyer, D., Herpertz, S., & Vocks, S. (2010). Reduction of gray matter density in the extrastriate body area in women with anorexia nervosa. Behavioural Brain Research, 206 (1), 63-67 DOI: 10.1016/j.bbr.2009.08.035

Thompson MA, Gray JJ. (1995). Development and validation of a new body-image assessment scale. J Pers Assess. 64:258-69.

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